(1) Field of the Invention
The present invention relates to an input apparatus for inputting coordinates to the screen and a display device having the same, and in particular, to a display device having an input apparatus of a capacitance coupling type, which is preferable for high precision in detecting coordinates.
(2) Related Art Statement
Display devices having an input apparatus (hereinafter referred to as touch sensor or touch panel) with a function of inputting through a screen where information is inputted through a touch operation on the display screen using a finger or the like of the user (contact or pressing operation, hereinafter simply referred to as touching) are used in mobile electronics, such as PDA's and portable terminals, various types of home electronics, and installed customer guiding terminals, such as automatic teller machines. As for these input apparatuses by means of touching, a resistance film system for detecting a change in the resistance value of the touched portion, a capacitance coupling system for detecting a change in the capacitance, and an optical sensor system for detecting a change in the amount of light of the portion that is blocked through touching are known.
The capacitance coupling system has the following advantages in comparison with the resistance film system and the optical sensor system. The capacitance coupling system is advantageous in that the display quality is not lowered due to transmittance, which is as high as approximately 90%, in comparison with the transmittance of the resistance film system and the optical sensor system, which are approximately 80%, for example. In addition, the capacitance coupling system is advantageous in durability because electrodes for detecting a signal do not make physical contact with other electrodes, while there is a risk with the resistance film system in that the resistance films may deteriorate or break because the touched point is detected through the physical contact of a resistance film.
An example of a touch panel of a capacitance coupling type is disclosed in the following Patent Document 1. In this disclosed system, electrodes for detecting a signal in the longitudinal direction (X electrodes) and electrodes for detecting a signal in the lateral direction (Y electrodes) are arranged in a two-dimensional matrix so that the capacitance of each electrode is detected in an input processing portion. In the case where a conductor, such as a finger, makes contact with the surface of the touch panel, the capacitance of the touched electrodes increases so that this is detected in the input processing portion, and the input coordinates are calculated on the basis of the signals resulting from the change in the capacitance detected by the electrodes. Here, the detection in the capacitance is not affected very much even when the resistance value, which is the physical property of the electrodes for detecting a signal, changes due to the deterioration of the electrodes, and therefore, the precision with the detection at the point of input on the touch panel is slightly affected. As a result, high precision with the detection at the point of input can be achieved.
Here, the Japanese Unexamined Patent Publication 2003-511799 can be cited as a prior art document that relates to the present invention.